Biology 105: Introduction to Genetics Page 1MidtermFall 2004

Name ____________________________

Student ID _______________________

Before starting, write your name on the top of each pageMake sure you have all 9 pages

You can use the back-side of the pages for scratch, but we will not grade answerswritten on the back-side of the page.

Part I Definitions20 points --------------------

Part II Short Answer25 points --------------------

Part III Multiple Choice26 points --------------------

Part IV Extended Calculation30 points --------------------

Total --------------------

Name ____________________________

Part I Definitions page 2

Hemizygous:

Prophase I:

Karyotype:

Interference:

Mitosis:

Name ____________________________Part II Short Answer (Answer 5 of the 6) page 3

Put an “X” through the question you DO NOT want graded

1. In humans, achondroplastic dwarfism and neurofibromatosis are extremelyrare autosomal dominant conditions. If a woman with achondroplasia marries a man withneurofibromatosis, what genotypes and phenotypes could be produced in their childrenand in what proportions? (these genes are unlinked)

2. A-------20MU--------------------B------5MU---------CAn AABBCC female is crossed to an aabbcc male and the resulting F1 progeny arebackcrossed to aabbcc individuals. What fraction of the F2 will be heterozygous forall three genes?

3. A unique species of fish containing only one large chromosome is discovered.Describe the ratios and classes of progeny (with respect to ploidy) produced when atriploid member of this species is crossed to a diploid member of this species.

Name ____________________________Short Answer continued page 4

4. For two genes far apart on the same chromosome, 50MU is the maximum mapdistance. Why?

5. A couple went to see a genetic counselor because each has a sibling affected withalbinism. Albinism is an autosomal recessive disease and neither member of thecouple nor any of their four parents is affected. What are the chances that their childwill be a carrier of albinism?

6. In genetically identical twin females heterozygote for a recessive X-linked eyedisease gene, it was discovered that one individual was normal while the other expresseda mild form of the disease. How can these results be explained?

Name ____________________________Page 5

Part III Multiple choice (make sure to write your selection in the space (________)provided at the beginning of each question

1. (_______) A variable feature of some chromosomes in corn is the presence orabsence of cytologically visible knobs. Suppose that one member of each of twopairs of chromosomes in a corn plant has a knob. If this plant were crossed with aknobless plant, what percentage of the offspring is expected to be knobless

a. 100%b. 75%c. 50%d. 25%e. 0%

2. (_______) Which of the following events occurs during mitosis but not meiosis?a. Segregation of sister chromatidsb. Pairing of homologous chromosomesc. Recombination between homologous chromosomesd. Alignment of chromosomes on the metaphase platee. none of the above

3. (_______) In the dihybrid cross AA bb x aa BB (A and B are unlinked gene),what proportion of the F2 offspring will be homozygous for the dominant formsof both genes?

a. 1/16b. 1/4c. 3/16d. 6/16e. 9/16

4. (_______) In four o'clock plants, the allele for red flowers is incompletelydominant over the allele for white flowers so that the heterozygotes are pink.What ratio of flower colors would you expect among the offspring, if pink flowersare crossed to red flowers?

a. 100% Pinkb. 25% Pink 75% Redc. 50% Pink 50% Redd. 75% Pink, 25% Rede. None of the above

Name ____________________________Multiple Choice continued page 6

5. (_______) Sister chromatids are genetically ___________, while homologouschromosome pairs are genetically ___________

a. similar, identicalb. distinct, identicalc. identical, identicald. identical, similare. none of the above

6. (_______) D. melanogaster has four pairs of chromosomes. Sperm from thisspecies are formed by a meiotic process in which homologous chromosomes pairand segregate but do not undergo recombination. How many genetically differentkinds of sperm could be produced by a D. melanogaster male?

a. 4b. 8c. 16d. 64e. 256

7. (_______) A trait which is passed father-to-son generation after generation ismost likely to be

a. X-linked recessiveb. X-linked dominantc. Autosomal recessived. Autosomal dominante. None of the above

8. (_______ ) All of these statements are true about mitosis excepta. results in two genetically identical productsb. occurs in the somatic cellsc. although recombination is rare, it occursd. homologs paire. sister chromatids segregate at anaphase

9. (________)A species of insect is discovered in which the rate of meioticrecombination is three times higher in females than males. By exclusivelymapping in males, genes A and C are found to be separated by 12MU. If themapping were performed in females the expected map distance would be:

a. 12MU d. 3MUb. 36MU e. need more informationc. 4MU

Name ____________________________Multiple Choice continued page 7

10. (_______) In the following pedigree, the indicated trait is caused by what type ofallele?

a. autosomal recessiveb. autosomal dominantc. X-linked recessived. X-linked dominante. Y-linked

11. (______) In the following pedigree, the indicated trait is caused by what type ofallele?

a. autosomal recessiveb. autosomal dominantc. X-linked recessived. X-linked dominante. Y-linked

12. (_______) What biological process does the Punnett Square represent?a. Segregation of sister chromatidsb. Segregation of homologous chromosomesc. Crossing over between homologous chromosomes during prophase I of

meiosisd. Independent alignment of different homologous pairs on the metaphase I

spindlee. Random fusion of sperm and eggs during fertilization

13. (_______)Mitotic recombination results in loss of heterozygousity froma. the point of recombination to the centromereb. the point of recombination to the telomerec. the centromere to the telomered. 15 MU past the point of recombinatione. 50 MU past the point of recombination

Name ____________________________Part IV Extended Calculation page 8

I. Sparkled eyes (sp) and wavy wings (wy) are autosomal recessive traits in Drosophila.A homozygous wild-type (normal) females was crossed to a sparkled, wavy male and theF1 males were then crossed to the F1 females to obtain the F2. Of 613 F2 obtained, 449were wildtype, 14 were sparkled, 15 were wavy and 135 were sparkled, wavy.Remember there is no recombination in Drosophila males.

A) Using a diagram explain the origin of these four classes

B) Determine the map distance between these two genes (show reasoning).

C) If recombination did occur in Drosophila males what additional phenotypic andgenotypic classes (if any) would be present in the F2. Explain your reasoning

Name ____________________________Extended Calculation continued Page 9

II. Large numbers of offspring from a cross of true-breeding no-wing female Drosophilato normal winged Drosophila males are scored (normal wing is dominant to no-wing).The following results are obtained: 1005 normal-winged females, 999 no-wing males, 3no-wing females, 2 normal wing males.

A) What chromosome are is the no-wing gene likely to reside on? Explain yourreasoning.

B) Using a diagram (punnett square), explain the origin of the two rare progeny classesdescribed above.

C) Describe a genetic or cytological experiment to test your proposed answer for part B